In microscope observations, microscope objective lenses having a long working distance as possible are demanded in consideration of preventing physical contacts with observation objects, a work efficiency, and the like. However, in ensuring a long working distance, it becomes difficult to correct various aberrations, especially high-order spherical aberration and chromatic aberration. Therefore, a microscope objective lens using a diffractive optical element (DOE) is proposed (For instance, refer to Patent Documents 1 and 2). In such a microscope objective lens, it becomes possible to sufficiently correct chromatic aberration, thus it is possible to focus on correcting spherical aberration etc. regarding corrections by a lens.
Generally, upon observations using microscopes, the microscopes are designed in a premise of conducting observations through a light-transmitting cover glass and glass dish which is disposed over an observation object (specimen). Upon designing microscopes, lenses are designed so that aberrations are restrained, by defining thickness and refractive index of the cover glass and glass dish disposed over the observation object, within a certain range in a state using a plate with refractive index and thickness defined as above. Accordingly, in case that the thickness and refractive index, etc. of the cover glass and glass dish disposed between an object and an objective lens are greatly different from a value as a criterion when designing, this causes degradation of image-forming performance, and this degradation tendency becomes more remarkable as a numerical aperture (N. A.) becomes large.
Then, it is publicly known a microscope objective lens having a mechanism to correct aberrations by changing part of lens distances in an objective lens depending on a variation of thickness, etc. of the cover glass and glass dish disposed between the objective lens and the observation object. Moreover, generally, since the glass dish had various shapes and materials and variability of each thickness is large, objective lenses are required to have sufficient aberration correcting performance by providing a large work distance, therefore objective lenses having a mechanism performing such an aberration correction are proposed (For instance, see Patent Document 3).